Split cycle engine

A method of controlling a recuperated split cycle internal combustion engine comprising:

• a compression cylinder accommodating a compression piston;
• a combustion cylinder accommodating a combustion piston;
• a crossover passage between the compression cylinder and the combustion cylinder arranged to provide compressed working fluid to the combustion cylinder from the compression cylinder;
• a coolant system arranged to regulate a temperature of the compressed working fluid supplied to the combustion cylinder from the compression cylinder through the crossover passage;
• and
• a recuperator arranged to heat compressed working fluid as the compressed working fluid flows from the compression cylinder to the combustion cylinder through the crossover passage;
• wherein the method comprises:
• receiving an indication of a peak temperature of combustion in the combustion cylinder;
• determining, based on the received indication, a peak temperature of combustion in the combustion cylinder;
• in response to determining that the peak temperature of combustion exceeds a selected threshold, controlling the coolant system to regulate the temperature of the compressed working fluid supplied to the combustion cylinder from the compression cylinder through the crossover passage so that a peak temperature of combustion in the combustion cylinder is less than the selected threshold;
• and
• wherein heating the compressed working fluid as the compressed working fluid flows from the compression cylinder to the combustion cylinder through the crossover passage comprises using the recuperator to recover heat from fluid exhausted from the combustion cylinder and using this recovered heat to heat the compressed working fluid as the compressed working fluid flows from the compression cylinder to the combustion cylinder through the crossover passage.